Biodiversity Strategy - Gosford City Council - NSW Government

Patonga Creek
Little information is available on Patonga Creek, other than a couple of unpublished reports
undertaken by students from Macquarie University in the late 1980's (Byrnes et al., 1987 and
Belford et al., 1989). Some of the information provided in these documents is erroneous. There
is a Council resolution to develop an Estuary Management Plan for Patonga Creek. This Plan
will ultimately guide management strategies for the creek and catchment.
Patonga Creek is approximately 8 km long and its catchment is mostly comprised of the
Brisbane Water National Park (13.4 km2). The estuary mouth has a constricted entrance due to
the accumulation of sand at the entrance. A breakwater was constructed to prevent closure but
requires dredging to maintain boat access.
Byrnes et al. (1987) indicate that the Creek has approximately 0.4 km2 of mangrove habitat with
small areas of associated saltmarsh and approximately 0.3 km2 of seagrass (Zostera
capricorni). They also provide a species list for fauna but by their own admission, the list is
incomplete and based only on opportunistic sightings by the project team.
Mangrove Creek
Little information is available for Mangrove Creek. There is a technical report on
macroinvertebrate assemblages in the freshwater reaches of the creek (Roberts, 2004). The
key relevant finding of this document is that there is a high level of diversity of
macroinvertebrates (waterbugs) in the creek.
In September 2004 the Hawkesbury Nepean Catchment Management Authority (CMA) began
preparation of the River Health Strategy, which will guide actions that will help to achieve the
river health targets in the CMAs Catchment Action Plan. Between October 2004 and June 2005,
a panel of community and technical experts undertook a rapid assessment of the economic,
social and environmental values of the river reach in the catchment and the threats to those
values. Mangrove Creek was included in this assessment process. The River Health Strategy
will help the CMA to make decisions about actions that are necessary to achieve improvements
in river health. The strategy will set broad priorities for on-ground works in the CMAs river
restoration program. It will provide detail about where in the catchment the actions need to take
place. It will be in operation for the 10 year period of the Catchment Action Plan. Although a
stand-alone document, the strategy is a key supporting document for the CMAs Catchment
Action Plan.
The assessment of the reach from the reservoir wall to the junction with Warren Creek and on to
the tidal reach (approximately 1 km upstream of Greengrove) indicates that the riparian
vegetation is of excellent quality and has an average width of 50 m. It also indicates that there is
a good diversity of macroinvertebrates. Threats to this reach include: channel modification;
barriers to ecosystem functioning because of a weir; flow regulation and modification; and exotic
riparian and aquatic plant species. There is also an issue with Koi carp above in the weir pool
and associated problems with turbidity. The assessment of the remaining reach down to the
Hawkesbury indicates poor riparian habitat due to extensive clearing. The major riparian
vegetation communities comprise of casuarinas, mangroves and saltmarsh. Threats are similar
to the upstream reach but also include boating activities and the grazing of livestock.
Brisbane Water
Brisbane Water is a broad shallow estuary located approximately 50 kilometres north of Sydney,
and is connected to Broken Bay by a relatively narrow channel and shoal on the western side
near the eastern end of Ocean Beach. It has an area of approximately 2800 hectares and
drains a catchment of roughly 190 square kilometres. The Estuary is complex in its morphology
and is subject to human modifications (e.g. the construction of St Hubert’s Island Canal Estate).
Biodiversity - Technical Report Page 140